A guide to calculating how much electricity a solar PV system will generate over a typical year. If you would prefer to talk to a member of the team please call us on 08448 150 200.
THE STANDARD ASSESSMENT PROCEDURE (SAP) CALCULATION FOR SOLAR PV
The government provides a standard method for calculating the amount of energy a PV system will supply over a year.
The equation is:
Predicted Generation (kWh/year) = Irradiance x Shading factor x kWp x 0.8
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Shading Factor: Unshaded - 1, Lightly Shaded - 0.8, Moderately Shaded - 0.6
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kWp: The kWp is the maximum power of your PV system. It represents the power that would be produced by the panels under standard lab conditions.
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Irradiance: Irradiance is the amount of energy that the roof receives from the sun. It depends on roof tilt and orientation, and can be found from the following table.
IMPROVING ON THE STANDARD ASSESSMENT PROCEDURE FOR SOLAR PV
The standard assessment procedure is useful - but it gives no idea of how much energy is produced over the course of the year. During summer months, PV panels produce about 5 times as much electricity as in the winter months - the sun is higher in the sky, the weather is clearer, and the days are longer. The graph below shows how the output from a 1kWp PV system in Nottingham will vary over the course of a typical year.
You can carry out your own assessment for any site in Europe using the online PVGIS tool.